1. Field of the Invention
The present invention relates to an organic electro luminescence display device and a fabricating method thereof, and more particularly to an organic electro luminescence display device that is adaptive for improving contrast ratio as well as improving the conductivity of an anode electrode, and a fabricating method thereof.
2. Description of the Related Art
Recently, there have been developed a variety of flat panel display devices that can reduce their weight and size, which are a disadvantage of a cathode ray tube CRT. The flat panel display device includes a liquid crystal display LCD, a field emission display FED, a plasma display panel PDP and an electro luminescence EL display device.
The PDP is relatively simple in its structure and fabricating process, thus it is advantageous in being made into a large size screen but there is a disadvantage in that its light emitting efficiency and brightness is low and its power consumption is high. The LCD is mainly used for a display device of a notebook computer so that its demand increases, but there is a disadvantage in that it is difficult to be made into a large size screen and its power consumption is high. Further, the LCD has a disadvantage in that there is high light loss by optical display devices such as polarizing filter, prism sheet, diffusion sheet and so on and its viewing angle is narrow. In comparison with this, the EL display device is largely divided into an inorganic EL and an organic EL and has an advantage in that the response speed is high and the light emitting efficiency, brightness and the viewing angle is high. Further, the organic EL display device might be able to display a picture with a high brightness of tens of thousands [cd/m2] at a voltage of about 10[V].
FIG. 1 is a perspective view representing a related art organic EL display device, FIG. 2 is a plane view specifically representing an A area of FIG. 1, and FIG. 3 is a sectional diagram of the organic EL display device taken along the lines I-I′ and II-II′ of FIG. 2.
The organic El display device shown in FIGS. 1 to 3 is formed on a substrate 2 for an anode electrode 4 and a cathode electrode 12 to cross each other.
A plurality of anode electrodes 4 are formed on the substrate 2 to be separated from each other with a designated gap.
An opaque conductive pattern 5 is formed on one side of the anode electrode 4. The opaque conductive pattern 5 plays the role of improving the conductivity of the anode electrode 4 which is formed of a transparent conductive material such as ITO (indium tin oxide), IZO (indium zinc oxide), ITZO (indium tin zinc oxide) having high resistance. An insulating film 6 having an aperture ratio is formed in each EL cell (E) area on the substrate 2 where the anode electrode 4 and the opaque conductive pattern 5 are formed.
A barrier rib 8 is located on the insulating film 6 for separating the organic light emitting layer 10 and the cathode electrode 12 which are to be formed thereon. The barrier rib 8 is formed in a direction of crossing the anode electrode 4 and has a reverse taper structure that an upper end part has a wide width than a lower end part. An organic light emitting layer 10 is formed on the insulating film 6 where the barrier rib 8 is formed, and the cathode electrode 12 is formed by depositing an electrode material on the entire surface.
The organic light emitting layer 10, as shown in FIG. 4, is formed by having a hole injection layer 10E, a hole transport layer 10D, a light emitting layer 10C, an electron transport layer 10B and an electron injection layer 10A deposited. The organic EL display device has electrons and holes emitted if a driving signal is applied to the anode electrode 4 and the cathode electrode 12, and the electron and hole emitted from the anode electrode 4 and the cathode electrode 12 are recombined within the light emitting layer 10C to generate a visible ray. At this moment, the generated visible ray exits to the outside through the anode electrode 4 to display a designated picture or image.
On the other hand, in the related art organic EL display device, there is still a problem in that the anode electrode 4 has a lower conductivity than the cathode electrode 12 which is formed of a metal of high conductivity such as aluminum AL even though the opaque conductive pattern 5 is formed for compensating the conductivity of the anode electrode 4, and the opaque conductive pattern 5 occupies part of a light emitting area P1 thus there is a problem in that the aperture ratio becomes smaller as much.
Further, in the related art organic EL display device, the light incident from the outside almost completely transmits the anode electrode 4 and the organic light emitting layer 10. As a result, when the light is emitted from the organic light emitting layer 10, an external light 40 being incident from the surface of the substrate 2 transmits the organic light emitting layer 10 and the anode electrode 4 of a transparent conductive material and is reflected by the cathode electrode 12 of a metal electrode, as shown in FIG. 5. Accordingly, there is a problem in that the contrast ratio is deteriorated.